1. The Field of the Invention
This invention relates generally to the administration of a supplemental, intermittent oxygen supply to a patient. More specifically, the present invention provides a method and apparatus for providing oxygen therapy to a patient, where a system includes the ability to conserve oxygen by only delivering an amount that is usable by the patient during an inspiration cycle.
2. The State of the Art
The state of the art in oxygen therapy is replete with systems that attempt to conserve oxygen being supplied to a patient. The need to conserve oxygen is a result of the understanding that continuous, long term oxygen therapy is expensive because of the large quantities of oxygen that needed to be provided to a patient.
Less sophisticated oxygen therapy systems provide oxygen at a continuous rate without interruption. The result is that all oxygen supplied to the patient during exhalation is wasted. This waste can be substantial considering that approximately two thirds of the respiratory cycle is spent in exhalation. Furthermore, these systems do not adjust for rates or depth of inspiration by the patient. These factors, combined with the fact that the oxygen therapy is generally being conducted using a mobile oxygen container, demonstrate the need for more prudent oxygen conservation. Clearly what is needed is a way to reduce oxygen consumption while maintaining adequate alveolar gas exchange of the patient.
To meet this need for oxygen conservation during oxygen therapy, systems have been developed which are designed to deliver oxygen only during patient inspiration. However, the methods and apparatus for accomplishing this goal are many, and are met with varying degrees of success.
One method for accomplishing conservation during oxygen therapy is to provide pulsed oxygen delivery to the patient according to some control logic based upon a physician prescribed gas flow rate and the breathing characteristics of the patient. For example, studies support the observation that the first portion of inspiration is the most effective time for oxygen delivery, with the last portion of the patient's inspiration not actually providing oxygen to the secondary respiratory system (i.e. the blood stream).
For example, in U.S. Pat. No. 5,165,397 issued to Arp, the patent apparently teaches a method and apparatus for providing oxygen on demand, where the system is responsive to a patient's breathing.
Similar systems are taught in U.S. Pat. No. 5,099,837 issued to Russel Sr. et al., and in U.S. Pat. No. 5,697,364 issued to Chua et al. All of these systems have numerous drawbacks which prevent them from serving all the functions of an acceptable oxygen conservation device. These drawbacks include, but are not limited to, a failure to adequately adapt to breathing depth (force) of the person using the system. They also fail to take into account changes that occur due to variations in altitude of the user. They also fail to compensate for changes in battery strength, and fail to adequately conserve battery power.
It would be advantageous over the state of the art in oxygen therapy to provide a conserving device which is responsive to the breathing rate of the patient. The system should adapt the volume of oxygen delivered depending upon depth of inspiration, and the rate of inspiration.
It would also be advantageous to provide a conserving device which did not require training of the patient, so that the system was responsive to the patient, and not the other way around.
The system should be capable of making some adjustments to patient inspiration, regardless of whether the patient's inspiration rate or depth changes rapidly.
It would also be an improvement over the state of the art to provide a system which does not require a plurality of oxygen delivery tubes between the conserving device and the patient.